MPC8280 datasheet(843/1386 Pages) FREESCALE

843 / 1386 page

Universal Serial Bus Controller

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

27-27

Data length (the second half word of a TxBD) is the number of octets the CP should send from this BD’s

data buffer. It is never modified by the CP.

Tx buffer pointer (the third and fourth half words of a TxBD) always points to the first location of the

buffer in internal or external memory. The pointer may be even or odd.

27.6.3

USB Transmit Buffer Descriptor (Tx BD) for Host

The Tx BD described in this section is used when the packet-level interface is active. See Section 27.5.1.1,

“Packet-Level Interface,” for more information.

Data to be transmitted with the USB to the CP by is arranged in buffers referenced by the Tx BD ring. The

first word of the Tx BD contains status and control bits.

CNF

Transmit confirmation. Valid only when the L bit is set; otherwise it is ignored.

Applies to multi-frame enabled endpoints (USEP

n[MF] = 1); refer to

Section 27.5.7.3, “USB Endpoint Registers (USEP1–USEP4).”

0 Continue to load the transmit FIFO with the next packet. Several packets may be

loaded to the FIFO.

1 Last packet that is loaded to FIFO. No more packets will be loaded to fifo after a

packet marked CNF, till it transmitted.

Reserved, should be cleared

8–9

PID

Packet ID. This bit field is valid for the first BD of a packet; otherwise it is ignored.

0X Do not append PID to the data.

10 Transmit DATA0 PID before sending the data.

11 Transmit DATA1 PID before sending the data.

10–12

—

Reserved, should be cleared

Time out. Indicates that the host failed to acknowledge the packet.

Underrun. Indicates that the USB encountered a transmitter underrun condition

while sending the buffer.

—

Reserved, should be cleared

0x02

0–15

Data length The data length is the number of octets that the CP should transmit from this BD’s

data buffer. It is never modified by the CP. This value should normally be greater than

zero.

0x04

0–31

Tx data

buffer

pointer

The transmit buffer pointer, which always points to the first location of the associated

data buffer, may be even or odd.The buffer may reside in either internal or external

memory.

Table 27-17. USB Function Tx BD Fields (continued)

Offset

Bit

Name

Description

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